Sampling results of a wells network to monitor a hydraulic barrier for seawater intrusion control at the Llobregat delta deep aquifer (Barcelona, Spain) are presented here for the period March 2007-2008. The monitoring programme consisted in periodical water sampling and piezometric level control in wells, local network and wastewater treatment plant. The first-phase results of the sampling campaign show a decrease in electric conductivity in the wells closer to the injection points. Also a cation exchange index decrease is observed, indicating a continuous increase in the water mixing process in the wells. Regarding emerging contaminants, enhanced wastewater treatment removed the majority of contaminants before injection. The preliminary field results of hydrogeological control of injected water indicate that improved pre-treatment of wastewater has been appropriate for contaminants removal.